The present invention relates generally to the data processing field, and more particularly, relates to a method and apparatus for implementing adaptive reordering of data recovery procedure steps in a direct access storage device (DASD).
Computers often include auxiliary memory storage units having media on which data can be written and from which data can be read for later use. DASDs or disk drive units incorporating stacked, commonly rotated rigid magnetic disks are used for storage of data in magnetic form on the disk surfaces. Data is recorded in concentric, radially spaced data information tracks arrayed on the surfaces of the disks. Transducer heads driven in a path toward and away from the disk axis of rotation write data to the disks and read data from the disks. Data located on a particular track on a disk surface is read or written by properly positioning a data transducer head directly over the track. In order to maintain the head in proper position over the data track, servo systems typically are incorporated into disk drives.
When problems arise detecting the customer data in a DASD, a data recovery procedure is started. All DASDs have operations or data recovery procedure (DRP) steps including multiple read operations that are performed in an attempt to correctly detect the customer data. FIG. 2 illustrates a conventional data recovery procedure for a disk drive. When an unsuccessful read operation is identified at decision block 204, then the DRP process is started. Predetermined file parameters are set based on the DRP step information at block 208 and the DRP step is performed. When an unsuccessful read operation for the DRP step is identified at decision block 210, then the DRP step is incremented to a next step in the DRP table. Then the predetermined file parameters are set based on this DRP step information at block 208 and the next DRP step is performed. As shown in FIG. 2, in known DASDs or disk drives, predefined data recovery procedure (DRP) steps are executed in a fixed order. For example, the first step is typically to read the same data on the next disk revolution, the 11th step might be to try to reset the magnetic head state by performing a dummy write. There may be, for example, 50 to 100 DRP steps used by a DASD or more DRP steps may be used depending on the architecture. The DRP steps are always the same and the process to retrieve the data follows the set of DRP steps in a fixed order.
A need exists for a mechanism to more efficiently implement data recovery procedures in a direct access storage device (DASD).
A principal object of the present invention is to provide a method and apparatus for implementing adaptive reordering of data recovery procedure steps in a direct access storage device (DASD). Other important objects of the present invention are to provide such method and apparatus for implementing adaptive reordering of data recovery procedure steps substantially without negative effect and that overcome many of the disadvantages of prior art arrangements.
In brief, a method and apparatus are provided for implementing adaptive reordering of data recovery procedure (DRP) steps in a direct access storage device (DASD). An initial set of DRP steps is stored. A reorder table is stored during the operation of the DASD. The reorder table includes data recovery data for each data head of successful predefined DRP step numbers. When a DRP process is started, checking for a modified DRP step is performed using the reorder table. Responsive to not identifying the modified DRP step, file parameters for a DRP read operation are set based on the initial set of DRP steps. Responsive to identifying the modified DRP step, file parameters for a DRP read operation are set based on a reordered DRP step that is identified by using the stored successful predefined DRP step numbers in the reorder table. When a successful DRP read operation is identified, the data recovery data in the reorder table are updated.
In accordance with features of the invention, the reordered DRP step is an identified most frequently occurring DRP step number in the reorder table for the current data head. The data recovery data for each data head stored in the reorder table includes a number of total errors, a number of errors above a set threshold, and a reorder flag. The reorder flag is set based upon the number of errors above the set threshold being at least a predefined percentage of the number of total errors. When the reorder flag is set, a reordered DRP step is identified using the stored successful predefined DRP step numbers in the reorder table.